提示SongBird instance has no attribute 'sound'

_metaclass_ = type class Bird: def _init_(self): self.hungry = True def eat(self): if self.hungry: print 'Aaaaa.....' self.hungry = False else: print 'No, think' class SongBird(Bird): def _init_(self): super(SongBird, self)._init_() self.sound = 'Squawk!' def sing(self): print self.sound sb = SongBird( ) sb.sing( )

刚开始学python，这是书上的代码。检查过很多遍，就是通不过。